Method for allocating pilots

ABSTRACT

There is provided a method for allocating pilots to a sub-frame. The sub-frame includes a plurality of blocks in time domain. The method includes allocating a data demodulation (DM) pilot used for demodulating data to two blocks spaced not contiguous with each other, and allocating a channel quality (CQ) pilot. System capacity can be increased, and degradation of performance incurred by a channel estimation error can be minimized.

TECHNICAL FIELD

The present invention relates to wireless communication, and morespecifically, to a method for allocating pilots to reduce channelestimation errors in a wireless communication system.

BACKGROUND ART

Third generation partnership project (3GPP) mobile communication systemsbased on a wideband code division multiple access (WCDMA) radio accesstechnique are widely spread all over the world. High speed downlinkpacket access (HSDPA) that can be defined as a first evolutionary stageof WCDMA provides 3GPP with a wireless access technique that is highlycompetitive in the mid-term future. However, since requirements andexpectations of users and service providers are continuously increasedand developments of competing radio access techniques are continuouslyin progress, new technical evolutions in 3GPP are required to securecompetitiveness in the future.

One of the systems being taken into consideration after the thirdgeneration is an orthogonal frequency division multiplexing (OFDM)system that can reduce the inter-symbol interference effect with lowcomplexity. The OFDM transforms serially inputted data symbols into Nparallel data symbols and transmits the parallel data symbols withloaded on N sub-carriers separated from each other. The sub-carriersmaintain orthogonality in terms of frequency. Each of orthogonalchannels experiences mutually independent frequency selective fading,and the spaces between transmitted symbols become wider, and thusinterference between the symbols can be minimized. Orthogonal frequencydivision multiple access (OFDMA) is a multiple access method thatrealizes a multiple-access by independently providing some of availablesub-carriers to each user in a system that uses OFDM as a modulationmethod. The OFDMA provides frequency resources, which are referred to assub-carriers, to each user, and each of the frequency resources areindependently provided to a plurality of users, and thus the frequencyresources are generally not overlapped with each other. As a result, thefrequency resources are mutual-exclusively allocated to each user.

One of the major problems of the OFDM/OFDMA is that peak amplitude of atransmission signal can be considerably higher than average amplitude.This peak-to-average power ratio (PAPR) problem is originated from thefact that an OFDM signal is the sum of N sinusoidal signals onsub-carriers different from each other. In order to save transmissionpower, it is needed to lower the PAPR.

One of the systems proposed to lower the PAPR is singlecarrier—frequency division multiple access (SC-FDMA). SC-FDMA is a typethat combines frequency division multiple access (FDMA) with existingsingle carrier—frequency division equalization (SC-FDE) method. TheSC-FDMA has a characteristic similar to that of the OFDMA in thatsignals are modulated and demodulated in a time domain and a frequencydomain using discrete Fourier transform (DFT), but it is advantageous insaving transmission power since the PAPR of a transmission signal islow. Particularly, in connection with usage of a battery, it isadvantageous for an uplink that connects a user equipment sensitive totransmission power to a base station.

In order to efficiently restore data at a receiver, channel informationshould be obtained. The channel information is used for modulating anddemodulating the data or scheduling users. Generally, the channelinformation is obtained based on a pilot contained in a signaltransmitted by a transmitter. However, an efficient pilot structure hasbeen not widely known yet.

DISCLOSURE OF INVENTION Technical Problem

An object of the invention is to provide a method for allocating pilotsto increase system capacity.

Technical Solution

In one aspect, there is provided a method for allocating pilots to asub-frame. The sub-frame includes a plurality of blocks in time domain.The method includes allocating a data demodulation (DM) pilot used fordemodulating data to two blocks spaced not contiguous with each other,and allocating a channel quality (CQ) pilot used for measuring channelquality to at least one block.

In another aspect, there is provided a method for allocating pilots to asub-frame. The sub-frame includes a plurality of blocks in time domain.The method includes allocating a DM pilot used for demodulating data toa first block, and allocating a CQ pilot used for uplink scheduling to asecond block, the second block not contiguous with the first block.

Advantageous Effects

System capacity can be increased, and degradation of performanceincurred by a channel estimation error can be minimized.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary view showing a mobile communication system.

FIG. 2 is a block diagram showing a transmitter according to anembodiment of the present invention.

FIG. 3 is an exemplary view showing a sub-frame transmitted by thetransmitter.

FIG. 4 is an exemplary view showing a signal structure of a CDM method.

FIG. 5 is an exemplary view showing a signal structure of an FDM-Lscheme.

FIG. 6 is an exemplary view showing a signal structure of an FDM-Dscheme.

FIG. 7 is an exemplary view showing a sub-frame structure when TTI=1 ms.

FIG. 8 is an exemplary view showing pilot allocation according to anembodiment of the present invention.

FIG. 9 is an exemplary view showing pilot allocation according toanother embodiment of the present invention.

FIG. 10 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIG. 11 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIG. 12 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIGS. 13 to 18 are exemplary views showing pilot allocation according tostill another embodiment of the present invention.

FIG. 19 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIGS. 20 to 25 are exemplary views showing pilot allocation according tostill another embodiment of the present invention.

FIG. 26 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIG. 27 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

FIG. 28 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

MODE FOR THE INVENTION

FIG. 1 is an exemplary view showing a mobile communication system.

Referring to FIG. 1, a mobile communication system comprises a basestation and a plurality of user equipments (UEs). This can be a singlecarrier—frequency division multiple access (SC-FDMA) system. The mobilecommunication system is widely deployed to provide a variety ofcommunication services such as voices, packet data, or the like.

The base station 10 generally is a fixed station that communicates withthe user equipment 20 and can be referred to as another terminology,such as a node-B, base transceiver system (BTS), access point, or thelike.

A user equipment 20 can be fixed or mobile and can be referred to asanother terminology, such as a mobile station (MS), user terminal (UT),subscriber station (SS), wireless device, or the like.

Hereinafter, downlink means a communication from the base station 10 tothe user equipment 20, and uplink means a communication from the userequipment 20 and the base station 10. In the downlink, a transmitter canbe a part of the base station 10, and a receiver can be a part of theuser equipment 20. In the uplink, a transmitter can be a part of theuser equipment 20, and a receiver can be a part of the base station 10.The base station 10 can include a plurality of receivers andtransmitters, and the user equipment 20 can include a plurality ofreceivers and transmitters.

FIG. 2 is a block diagram showing a transmitter according to anembodiment of the present invention.

Referring to FIG. 2, the transmitter 100 incldues a discrete Fouriertransform (DFT) unit 110, a sub-carrier mapper 120, an inverse fastFourier transform (IFFT) unit 130, and a cyclic prefix (CP) insert unit140.

The DFT unit 110 performs DFT on an input signal s and transforms theinput signal into frequency domain signals x. If it is assumed that Nbis the number of sub-carriers for a certain user, the operation of theDFT unit 110 can be expressed as shown

x=F _(Nb×Nb)s  MathFigure 1

where F_(Nb×Nb) is a DFT matrix having a size of Nb used for spreadingdata symbols.

The sub-carrier mapper 120 performs sub-carrier mapping on spreadedfrequency domain signals x in a certain sub-carrier allocation method.The IFFT unit 130 performs IFFT on signals x′ allocated by thesub-carrier mapper 120 and converts the signals into a time domainsignal y. The time domain signal y can be said as an OFDM symbol, whichcan be expressed as shown

The sub-carrier mapper 120 performs sub-carrier mapping on spreadedfrequency domain signals x in a certain sub-carrier allocation method.The IFFT unit 130 performs IFFT on signals x′ allocated by thesub-carrier mapper 120 and converts the signals into a time domainsignal y. The time domain signal y can be said as an OFDM symbol, whichcan be expressed as shown

y=F ⁻¹ _(N×N) x ¹  MathFigure 2

where F′ _(N×N) is an IFFT matrix having a size of N, which is used fortransforming a frequency domain signal into a time domain signal.

The CP insert unit 140 inserts a CP into the time domain signal y, andthe CP-inserted signal is converted into an analog signal by the RF unit150 and propagated into a radio channel through an antenna 160. Themethod of generating a transmission signal and transmitting thetransmission signal to the receiver by the transmitter is referred to asSC-FDMA. The size of the DFT or IFFT matrix can be varied.

FIG. 3 is an exemplary view showing a sub-frame transmitted by thetransmitter. The length of the sub-frame can be called as a transmissiontime interval (TTI). Here, the TT1 is 0.5 millisecond (ms), but notlimited to.

Referring to FIG. 3, a sub-frame contains six long blocks (LB) and twoshort blocks (SB). The long block LB is a block having a time intervallonger than that of the short block SB. Neither the long block LB northe short block SB has an absolute size. The short block SB includes afirst short block SB#1 and a second short block SB#2. Here, the firstshort block SB#1 precedes the second short block SB#2 in the aspect oftime. That is, the first short block SB#1 is transmitted prior to thesecond short block SB#2.

Although the long block LB is used for control and/or data transmission,it also can be used for transmitting a reference signal. The referencesignal is also called as a pilot. If the pilot is contained in the longblock LB, the long block LB can be referred to as a pilot block. Theshort block SB can be used for control and/or data transmission or canbe used for transmitting a pilot. If the pilot is contained in the shortblock SB, the short block SB can be referred to as a pilot block. Acyclic prefix (CP) is inserted in each of the long block LB and theshort block SB to minimize interference between symbols and interferenceoccurred by multiple path channel.

The time interval of the short block SB can be shorter than the timeinterval of the long block LB. The time interval of the short block SBis not limited, but it can be preferably 0.5 times of the time intervalof the long block LB. Due to duality of the time domain and frequencydomain, the frequency band of the short block SB is twice as wide as thefrequency band of the long block LB if the time interval of the shortblock SB is 0.5 times of the time interval of the long block LB. Inaddition, the number of sub-carriers of the long block LB is twice asmany as the number of sub-carriers of the short block SB. In order toclarify the explanation, hereinafter, it is assumed that the timeinterval of the short block SB is 0.5 times of the time interval of thelong block LB.

Although the time interval of the first short block SB#1 is the same asthe time interval of the second short block SB#2, it is not alimitation, but they can have time intervals different from each other.In addition, the time interval of the short block SB can be dynamicallymodified depending on the time interval of the long block LB or asituation of a system.

A sub-frame contains six long blocks LB and two short blocks SB, but thenumber of the long blocks and the short blocks contain in the sub-frameis not limited. The sub-frame may contain at least one long block and atleast one short block.

Although four long blocks LB are arranged between two short blocks SB inthe sub-frame, the arrangement of the short blocks SB and the longblocks is not limited, but can be diversely modified depending on asystem. For example, three long blocks LB can be arranged between shortblocks SB, or five long blocks LB can be arranged. In addition,arrangement of the short blocks SB can be dynamically modified withinthe sub-frame depending on performance or environment of a system.

A pilot is data previously known between the transmitter and thereceiver and can be classified into two types depending on its usage.One is a channel quality (CQ) pilot for measuring channel quality inorder to schedule users and to apply an adaptive modulation and coding(AMC) scheme. The other is a data demodulation (DM) pilot for estimatinga channel in order to demodulate data. The CQ pilot is transmitted at apredetermined time in the frequency domain, and the base station graspsthe channel state of the user equipment using this information andschedules user equipments in a predetermined scheduling method.Accordingly, for uplink scheduling of the base station, creating a largenumber of orthogonal channels within a limited time and frequency domainso that a large number of user equipments within a cell may transmit CQpilots will affect capacity of the system. On the other hand, the DMpilot is a pilot that is transmitted within the time and frequencydomain when the user equipment is scheduled and transmits data in thetime and frequency domain.

A pilot can be categorized into a CQ pilot and a DM pilot by usage. Itis general that the pilot is the DM pilot if the pilot is transmittedwithin the frequency band of a corresponding user equipment, whereas thepilot is the CQ pilot if the pilot is transmitted throughout a frequencyband scheduled wider than the frequency band of the user equipment bythe base station. Accordingly, when the pilot is used as the CQ pilot,it can also be used as the DM pilot.

Since there are a plurality of user equipments in a base station or in asector, each user equipment needs to be discriminated. Particularly, apilot block should be distinguished between user equipments by usingorthogonality.

The orthogonality is divided into a time domain orthogonality, afrequency domain orthogonality, and a code domain orthogonality. Thetime domain orthogonality has a problem in that an accurate transmissiontiming control is needed. Accordingly, in an SC-FDNA system, thefrequency domain orthogonality or the code domain orthogonality has afurther superior characteristic.

The frequency domain orthogonality can be accomplished by transmitting asignal of each of user equipment through a different sub-carrier.Hereinafter, a signal structure using a signal orthogonal in thefrequency domain is referred to as frequency division multiplexing(FDM). In the FDM, frequency bands of respective user equipmentsallocated to a sub-carrier are not overlapped with each other. Thefrequency domain orthogonality can be applied to a localized signalstructure or a distributed signal structure. A localized signal occupiescontinuous spectrums, and a distributed signal occupies comb-shapedspectrums. Hereinafter, a signal structure using the localized signal isreferred to as frequency division multiplexing ? localized (FDM-L), anda signal structure using the distributed signal is referred to asfrequency division multiplexing ? distributed (FDM-D).

The code domain orthogonality is accomplished by transmitting a signalof each user equipment through a common sub-carrier. The entire or aportion of a frequency band allocated to a sub-carrier for each userequipment is overlapped. Hereinafter, a signal structure using a signalorthogonal in the code domain is referred to as code divisionmultiplexing (CDM).

FIG. 4 is an exemplary view showing a signal structure of a CDM method.

Referring to FIG. 4, sub-carriers of a pilot signal are transmitted inan overlapped manner for M users (user equipments). The pilot is loadedon the short block SB, and the CDM performs multiplexing among userequipments through the code orthogonality by allocating a code sequenceto the entire bands of the short block SB.

Sub-carriers of the short block SB can be allocated throughout theoverall frequency band. Here, the overall frequency band is a frequencyband including all frequency bands of the user equipments scheduledwithin a base station or a sector. The short block SB is in the form ofoverlapped frequency bands of user equipments. The short block SBmaintains orthogonality of each user equipment in the code domain.

A constant amplitude zero auto-correlation (CAZAC) sequence can be usedas a code sequence. Generally, there are two types of CAZAC sequences, aGCL CAZAC and a Zadoff-Chu CAZAC. The two types of sequences are in aconjugate relation. For example, the Zadoff-Chu CAZAC can be obtained byapplying a conjugate to the GCL CAZAC.

In the Zadoff-Chu CAZAC, the k-th entry CAZAC sequence can be expressedas shown

$\begin{matrix}{{{c\left( {{k;N},M} \right)} = {\exp \left\{ \frac{{j\pi}\; {{Mk}\left( {k + 1} \right)}}{N} \right\} \mspace{31mu} {for}\mspace{14mu} N{\mspace{11mu} \;}{is}\mspace{14mu} {odd}}}{{c\left( {{k;N},M} \right)} = {\exp \left\{ \frac{{j\pi}\; {Mk}^{2}}{N} \right\} \mspace{31mu} {for}\mspace{14mu} N{\mspace{11mu} \;}{is}\mspace{14mu} {even}}}} & {{MathFigure}\mspace{14mu} 3}\end{matrix}$

where M denotes a root index and N denotes the length of a CAZACsequence. M is a prime relative to N.

The CAZAC sequence c(k;M,N) has three characteristics described below.

$\begin{matrix}{{{{c\left( {{k;N},M} \right)}} = {1\mspace{31mu} {for}\mspace{14mu} {all}\mspace{14mu} k}},N,M} & {{MathFigure}\mspace{14mu} 4} \\{{R_{M;N}(d)} = \left\{ \begin{matrix}{1,} & {{{for}\mspace{14mu} d} = 0} \\{0,} & {{{for}\mspace{14mu} d} \neq 0}\end{matrix} \right.} & {{MathFigure}\mspace{14mu} 5} \\{{{R_{M_{1},{M_{2};N}}(d)} = {p\mspace{31mu} {for}\mspace{14mu} {all}\mspace{14mu} M_{1}}},M_{2}} & {{MathFigure}\mspace{14mu} 6}\end{matrix}$

Equation 4 means that the size of the CAZAC sequence is always one.Equation 5 means that auto correlation of the CAZAC sequence isexpressed as a Dirac-delta function. The auto correlation is based oncircular correlation. Equation 6 means that the cross correlation isalways a constant.

A pilot signal loaded on the short block SB can be used as a DM pilotfor demodulating a data signal transmitted on a sub-carrier of a longblock of the same band. In addition, since this pilot signal istransmitted throughout the overall frequency band, it can be used as aCQ pilot for measuring channel quality.

FIG. 5 is an exemplary view showing a signal structure of an FDM-Lscheme.

Referring to FIG. 5, sub-carriers are locally concentrated for M users(user equipments). Different user equipments are allocated to differentfrequency bands, and frequency division multiplexing is used.

Sub-carriers are locally concentrated in the short block SB and the longblock LB for each user equipment. A pilot is loaded on the sub-carrierof the short block SB. If the time interval of the short block SB is 0.5times of the time interval of the long block LB, the sub-carrier of theshort block SB occupies a band twice as wide as that of the sub-carrierof the long block LB. Accordingly, two contiguous sub-carriers of thelong block LB make a pair with one sub-carrier of the short block SB.

In the FDM-L scheme, a pilot signal loaded on the short block SB can beused as a DM pilot for demodulating a data signal transmitted on thesub-carrier of the long block LB of the same band. It is since that thefrequency band of the sub-carrier of the short block SB is overlappedwith that of the sub-carrier of the long block LB. However, since thepilot signal is locally concentrated in the frequency domain for acorresponding user equipment, it is difficult to be used as a CQ pilotfor measuring channel quality of the overall frequency band.

FIG. 6 is an exemplary view showing a signal structure of an FDM-Dscheme.

Referring to FIG. 6, sub-carriers are distributed and non-contiguous forM users (user equipments). Sub-carriers of the long block LB and theshort block SB are allocated to be distributed at regular intervals sothat sub-carriers of the same user equipment are not to be contiguous.That is, sub-carriers of a user equipment are distributed at regularintervals.

Pilot signals allocated to the first short block SB#1 and the secondshort block SB#2 are allocated in the frequency domain to be staggeredfrom each other for respective user equipments. If the time interval ofthe short block SB is 0.5 times of the time interval of the long blockLB, the sub-carrier of the short block SB occupies a band twice as wideas the band of the a sub-carrier of the long block LB. Since twofrequency bands of the long block LB are arranged in one frequency bandof the short block SB, in the FDM-D scheme, pilot signals of two shortblocks SB are alternatively allocated for each user equipment withrespect to the location of a sub-carrier of a user equipmentcorresponding to the long block LB. For example, a pilot signal for afirst user equipment 302 of the long block LB is loaded on thesub-carrier 301 of the first short block SB#1. A pilot signal for asecond user equipment 303 of the long block LB in the same band isloaded on the sub-carrier 304 of the second short block SB#2.Thereafter, pilot signals are loaded on the sub-carriers of the shortblock SB for respective user equipments of the long block LB in asubsequently staggered form.

In the FDM-D scheme, a pilot signal loaded on the short block SB can beused as a DM pilot for demodulating a data signal transmitted on thesub-carrier of the long block LB of the same band. It is since that thefrequency band of the sub-carrier of the short band SB is overlappedwith the frequency band of the sub-carrier of the long block LB. Inaddition, since this pilot signal is transmitted throughout the overallfrequency band, it can be used as a CQ pilot for measuring channelquality.

In the FDM-D scheme, only a pilot signal of either the first short blockSB#1 or the second short block SB#2 can be used at the location of asub-carrier to which data of the long block LB is allocated. Therefore,an interpolation cannot be performed on the axis of time, anddegradation of performance is invited in a time selective channelenvironment in which moving speed of a user equipment is high.

When a 0.5 ms TTI is assumed, one sub-frame becomes one TTI. However, ifthe TTI is expanded to 1 ms, it becomes a different matter.

FIG. 7 is an exemplary view showing a sub-frame structure when TTI=1 ms.

Referring to FIG. 7, it is a form of repeating the sub-frame of FIG. 3under the assumption that the same sub-frame is maintained. There are 12long blocks LB for transmitting data and 4 short blocks SB fortransmitting pilots.

One of the problems of the sub-frame structure is that although CQpilots are allocated to all resources, i.e., all sub-carriers,corresponding to the short block SB, the number of user equipments thatcan be multiplexed is limited. That is, since the number of sub-carriersallocated to one short block SB is only a half of the number ofsub-carriers allocated to one long block LB, the length of a CAZACsequence is short, and thus the number of cases where circulation isdelayed is limited. Furthermore, if DM pilots and CQ pilots aremultiplexed within the same short block SB in the FDM scheme, intervalsof sub-carriers of the CQ pilot are increased, and thus the number ofCAZAC sequences is decreased, which makes cell planning difficult as aresult. Due to distribution of power for DM pilots and CQ pilots anddecrease of the intervals of sub-carriers on the frequency domain,performance of channel estimation also can be degraded.

In addition, as an example, three short blocks SB out of four shortblocks SB can be used as a DM pilot for demodulating data, and the otherone short block SB can be used as a CQ pilot for scheduling thefrequency domain. At this point, since only one short block SB is usedas a CQ pilot, time spacing between short blocks SB that exist betweentwo sub-frames is not uniform, and thus efficiency of channel estimationcan be dropped. Furthermore, if CQ pilots are multiplexed among userequipments in the CDM scheme, the number of user equipments that can bemultiplexed is limited by a CAZAC sequence.

Hereinafter, a method of allocating pilots according to the presentinvention will be described.

FIG. 8 is an exemplary view showing pilot allocation according to anembodiment of the present invention.

Referring to FIG. 8, the sub-frame contains 13 long blocks LB and 2short blocks SB. Comparing with the sub-frame of FIG. 7, two shortblocks SB are modified to one long block LB.

The two short blocks SB can be used as a DM pilot, and the one longblock LB#7 can be used as a CQ pilot. That is, sub-carriers areallocated to the short blocks SB throughout the frequency band of aspecific user equipment, and sub-carriers are allocated to the longblock LB#7 throughout a frequency band containing the frequency band ofa specific user equipment.

Although a long block LB#7 at the center is selected as a long block LBused as a pilot block, a long block LB at another position can beselected. The two short blocks SB can be arranged at positionsrespectively apart from the long block LB#7, which is used as a pilotblock, in the opposite directions. In this case, time spacing betweenpilots is maintained, and thus efficiency of channel estimation can beenhanced. For example, the two short blocks SB are respectively arrangedfive long blocks away from the long block LB#7 in the oppositedirections. The space between the long block LB#7, i.e., a pilot block,and the short block can be appropriately modified depending onsituations.

The short blocks SB can build orthogonality among user equipments in FDMor CDM. The long block LB#7 can build orthogonality among userequipments in CDM. A CAZAV sequence can be used in the short blocks SBand the long block LB#7. At this point, the short blocks SB can buildorthogonality among user equipments within a cell in FDM, and can buildorthogonality among user equipments in different cells in CDM.

If a user equipment is identified in the CDM scheme since the long blockLB#7 twice as wide as the short block SB is used as a CQ pilot, the basestation can multiplex twice as many user equipments. It is since thatthe number of codes of a CAZAC sequence depends on the length of thesequence. Furthermore, it is advantageous in allocating sequencesbetween adjacent cells. In addition, as the length of the sequencebecomes longer due to the characteristic of the CAZAC sequence, a crosscorrelation value becomes smaller, and thus a processing gain also canbe obtained accordingly.

The long blocks LB#7 used as a CQ pilot also can be multiplexed among aplurality of user equipments in the CDM or FDM scheme. Since channelquality is measured throughout the overall frequency band, it ispossible to know a channel estimation value for a data transmission bandused for the long block LB (excluding the long block LB#7 used as apilot block) to which a sub-carrier transmitted in a localized form isallocated. Accordingly, a pilot contained in the long block LB#7 alsocan be used as a DM pilot for demodulation.

In the method described above, since two short blocks SB are convertedinto one long block LB, a length corresponding to one CP allocated tothe long block LB remains, and thus the length of the CP needs to bereadjusted. In an embodiment, the length of the one remaining CP can beuniformly allocated to all CPs within a 1 ms TTI. Therefore, a delayspread of a channel that is larger than that of an existing structurecan be covered. In another embodiment, the one remaining CP is allocatedto a pilot block. For example, the CP is allocated to the long blockLB#7 or a short block SB to which a CQ pilot is allocated. Therefore, afurther larger margin is put in a pilot block to which a pilot isallocated, and thus deviated timing can be further easily updated.

FIG. 9 is an exemplary view showing pilot allocation according toanother embodiment of the present invention.

Referring to FIG. 9, in comparison with the sub-frame of FIG. 8, shortblocks SB are arranged at both ends. Two short blocks SB arerespectively arranged six long blocks away from the long block LB#7 inthe opposite directions. The short blocks SB can be used as a DM pilot,and the one ling block LB#7 can be used as a CQ pilot.

FIG. 10 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 10, two short blocks SB and two long blocks LB#6 andLB#12 are used as a pilot within a 1 ms TTI. The short blocks are usedas a DM pilot. The long blocks LB#6 and LB#12 are used as a CQ pilot. Inaddition, since the long blocks LB#6 and LB#12 contain the frequencyband of a specific user equipment, they also can be used as a DM pilot,as well as a CQ pilot.

If the long blocks LB#6 and LB#12 twice as wide as the short blocks SBare used as a pilot, and thus user equipments are multiplexed for CQpilots in the CDM scheme, system capacity can be increased compared withusing the short blocks SB. In addition, since two long blocks LB#6 andLB#12 are used as a pilot, accuracy of CQ measurement and/or channelestimation can be enhanced.

FIG. 11 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 11, the positions of long blocks LB#5 and LB#11 onwhich pilots are loaded are modified from the sub-frame of FIG. 10. Thearrangement of two short blocks SB and two long blocks LB#5 and LB#11 isnot limited as shown in the figure, but can be diversely modified.

FIG. 12 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 12, the long block LB#13 positioned at the end of thesub-frame is used as a CQ pilot, and two short blocks SB and one longblock LB#5 are used as a DM pilot. This is a case where the long blockLB#13 positioned at the end of the sub-frame is used throughout theentire bands. If the CDM scheme is used to identify a user equipment,the long block LB#13 can estimate channels of entire bands, and thus itcan be used as a DM pilot, as well as a CQ pilot. Even when the FDMscheme is used to identify a user equipment, the long block LB#13 canestimate channels of entire bands, and thus it can be used as a DMpilot, as well as a CQ pilot.

FIGS. 13 to 18 are exemplary views showing pilot allocation according tostill another embodiment of the present invention.

Referring to FIGS. 13 to 18, the long block LB#13 positioned at the endof the sub-frame is used as a CQ pilot, and two short blocks SB and onelong block LB#5 are used as a DM pilot. FIGS. 13 to 18 shows sub-framesin which positions of the short blocks and the long block used as a DMpilot are modified. Pilots are allocated while maintaining the timespace between the short blocks SB and the long block on which the pilotsare loaded so that channel estimation performance can be maintained inaccordance with changes in time.

The two short blocks SB and one long block on which DM pilots are loadedare not limited to the forms shown in the figures, but can be diverselymodified.

Hereinafter, a method of allocating pilots to a sub-frame configuresonly with long blocks. That is, one sub-frame is configured with aplurality of blocks having a uniform length.

FIG. 19 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 19, pilots are loaded on two long blocks LB#4 andLB#11, and at least one of the long blocks is used as a CQ pilot. Forexample, a fourth long block LB#4 is used as a DM pilot, and an eleventhlong block LB#11 is used as a CQ pilot. Alternatively, the fourth longblock LB#4 is used as a CQ pilot, and the eleventh long block LB#11 isused as a DM pilot. Both of the two long blocks LB#4 and LB#11 can beused as a CQ pilot. It is since that a CQ pilot also can be used as a DMpilot.

The two long blocks LB#4 and LB#11 can be used as a DM pilot, and one ofthe other long blocks can be used as a CQ pilot. For example, the fourthlong block LB#4 and the eleventh long block LB#11 can be used as a DMpilot, and a first long block LB#1 can be used as a CQ pilot.Alternatively, the fourth long block LB#4 and the eleventh long blockLB#11 can be used as a DM pilot, and a fourteenth long block LB#14 canbe used as a CQ pilot. At this point, the interval of CQ pilots is equalto or longer than the interval of DM pilots. For example, CQ pilots canbe allocated to long blocks at intervals of 1 TTI or longer than 1 TTI.

If only long blocks LB#4 and LB#11 are used as pilot blocks, and the CDMscheme is used, the number of codes of a CAZAC sequence can beincreased, and thus system capacity is increased. In addition, thenumber of long blocks is increased by converting two short blocks intoone long block, and thus a data rate can be increased.

FIGS. 20 to 25 are exemplary views showing pilot allocation according tostill another embodiment of the present invention.

Referring to FIGS. 20 to 25, various arrangements of two long blocks onwhich pilots are loaded are shown. Pilots are allocated whilemaintaining the time space between long blocks on which the pilots areloaded so that channel estimation performance can be maintained inaccordance with changes in time.

The long blocks on which pilots are loaded are not limited to the formsshown in the figures, but can be diversely modified. In addition, thenumber of long blocks on which pilots are loaded is not limited to two,but pilots can be loaded on one or more long blocks.

FIG. 26 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 26, pilots are loaded on two long blocks LB#1 andLB#13 and two short blocks SB#1 and SB#2. Pilots are loaded on the longblocks LB#1 and LB#13 positioned at both ends of 1 ms TTI.

The pilots of the long blocks LB#1 and LB#13 can be used as a DM pilot,and since pilots of the short blocks SB#1 and SB#2 are allocated withina scheduling bandwidth containing the frequency band of a specific userequipment or for the entire bands, they can be used both as a CQ pilotand as a DM pilot. Since the long blocks LB#1 and LB#13 twice as wide asthe short blocks SB#1 and SB#2 are used as a DM pilot, accuracy ofchannel estimation can be enhanced on the axis of frequency.

FIG. 27 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 27, pilots are loaded on two long blocks LB#2 andLB#12 and two short blocks SB#1 and SB#2. Compared with the embodimentof FIG. 26, pilots are loaded on the long blocks LB#2 and LB#12respectively positioned at one long block inside from both ends of 1 msTTI. Pilots of the long blocks LB#2 and LB#12 can be used as a DM pilot,and since pilots of the short blocks SB#1 and SB#2 are allocated withina scheduling bandwidth containing the frequency band of a specific userequipment or for the entire bands, they can be used both as a CQ pilotand as a DM pilot.

FIG. 28 is an exemplary view showing pilot allocation according to stillanother embodiment of the present invention.

Referring to FIG. 28, pilots are loaded on two long blocks LB#3 andLB#11 and two short blocks SB#1 and SB#2. Pilots of the long blocks LB#3and LB#11 can be used as a DM pilot, and since pilots of the shortblocks SB#1 and SB#2 are allocated within a scheduling bandwidthcontaining the frequency band of a specific user equipment or for theentire bands, they can be used both as a CQ pilot and as a DM pilot.

The steps of a method described in connection with the embodimentsdisclosed herein may be implemented by hardware, software or acombination thereof. The hardware may be implemented by an applicationspecific integrated circuit (ASIC) that is designed to perform the abovefunction, a digital signal processing (DSP), a programmable logic device(PLD), a field programmable gate array (FPGA), a processor, acontroller, a microprocessor, the other electronic unit, or acombination thereof. A module for performing the above function mayimplement the software. The software may be stored in a memory unit andexecuted by a processor. The memory unit or the processor may employ avariety of means that is well known to those skilled in the art.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims. Therefore, allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are intended to beembraced by the appended claims.

1-7. (canceled)
 8. A method of transmitting a frame, the methodcomprising: allocating a first block and at least one second block intothe frame having a plurality of symbols, wherein the first blocktransmits first symbol for first pilot signaling, and the at least onesecond block transmits at least one second symbol for second pilotsignaling, wherein the first block is used for control transmission andthe at least one second block is used for a channel estimation in orderto demodulate data in the frame, wherein a length of the first block isshorter than a length of the at least one second block in a time domain;transmitting the first block; and transmitting the at least one secondblock, wherein the at least one second block further transmits the data.9. The method of claim 8, wherein a number of subcarriers of the firstblock is less than a number of subcarriers of the at least one secondblock.
 10. The method of claim 8, wherein the first block and the atleast one second block are distinguishable by a receiver.
 11. The methodof claim 8, wherein the first symbol for first pilot signaling istransmitted at a predetermined time.
 12. An apparatus of transmitting aframe, the apparatus comprising: a transmitter for transmitting firstblock; and a transmitter for transmitting at least one second block,wherein the first block and the at least one second block are allocatedinto the frame having a plurality of symbols, wherein the first blocktransmits first symbol for first pilot signaling, and the at least onesecond block transmits at least one second symbol for second pilotsignaling, wherein the first block is used for control transmission andthe at least one second block is used for a channel estimation in orderto demodulate data in the frame, wherein a length of the first block isshorter than a length of the at least one second block in a time domain,wherein the at least one second block further transmits the data. 13.The apparatus of claim 12, wherein a number of subcarriers of the firstblock is less than a number of subcarriers of the at least one secondblock.
 14. The apparatus of claim 12, wherein the first block and the atleast one second block are distinguishable by a receiver.
 15. Theapparatus of claim 12, wherein the first symbol for first pilotsignaling is transmitted at a predetermined time.